Thanks for the information David. I will look up ITU-J.83B ... Do you happen to have any captured QAM cable data (or any website that lists the data) ? I wanted to see if I can put together a software demod for digital cable ...
On 8/13/07, David I. Emery <[EMAIL PROTECTED]> wrote: > On Mon, Aug 13, 2007 at 10:52:54AM -0400, Vijay Ramasami wrote: > > Hi, > > > > I have a couple of questions: > > > > 1. Does the US digital cable system follow the DVB-C standard (or one > > of its annexes) ? Is there any information (website) on the typical > > symbol rates, bandwidths (I am guessing approx 6 MHz), used ? > > There is a Cablelabs spec that defines what is used. The ETSI > standards (ITU-T J.83B) also define the particular parameters as well. > > I can look up detailed references if needed... > > The are actually only two standard modulations in wide use 64QAM > with a particular set of parameters that yields a 30 Mb/s signal with a > 5.056941 Msym/symbol rate and a 256QAM signal which yields a 38.9 Mb/s > signal with a symbol rate of 5.360537 Msym/s > > Both signals are 6 MHz wide as US CATV is universally 6 MHz > channel based. > > > 2. Has anyone successfully captured (preferably unencrypted) digital > > QAM transmissions using the USRP ? If so, can you please send me a > > link to the data ? Given that the symbol rates are in the range of 5-6 > > Ms/s, it must be possible to use 16 MHz sampling frequency to > > demodulate the signals. > > > > I have used a number of purpose built demods, but not yet tried > a USRP solution. Some of the cable transport streams have open > channels, but you will find most are encrypted except the local OTA HD > signals and a few freebie promos. > > It is also possible to MODULATE QAM cable standard signals, > something that gets more useful every month as more QAM/ATSC tuners are > shipped for cable ready setups with CableCards rather than set top > boxes. This of course allows direct input of MPEG transport streams > into the digital domain of LCD/plasma panels with no analog step... > > > -- > Dave Emery N1PRE/AE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass 02493 > "An empty zombie mind with a forlorn barely readable weatherbeaten > 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in > celebration of what could have been, but wasn't and is not to be now either." > > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
